Check out alltubetesters dot com. I have no affiliation and have never dealt with them, and they are across the country, but I know they do that kind of work.
Call the local music stores. They still sell tube gear and they almost always have someone that repair(s) the guitar amps, etc. They will usually repair or calibrate tube testers. There is another place that started out selling used gear but they now carry new gear. I believe the name is Hi-Tech. When I lived there they would work on tube gear, etc. And there is Angela Instruments out past Laurel,MD. He may be able to assist you. Good luck! Lastly, search Ebay for tube tester calibration. There is a place in Wilmington, N.C. that does just that. I found them last week while searching for a B&K tube tester.
Go to Ebay and type in this number under the Ebay Search
280177488657 It will be for a B&K 747 calibration service.
They may have manuals, etc. I know they can perform the service. The calibration may not be hard but if your unit requires tubes you have to have the calibration tube in it. If it is solid state it may be much easier and maybe not require anything but the turn of a few buttons. Do a google search for the model you have along with the word manual and you should get some hits. Ctech may be able to help too.
Alltubes.com is a nice site too. I've been there before as well. You may be able to get a manual from them there.